Service dogs are dogs that have been individually trained to perform a specific task for individuals who have disabilities. The disabilities can vary greatly, and so do the tasks that the service dogs perform.

Service dogs are often identified by wearing a service dog vest or tag, letting the public know that it is a service dog; otherwise, their handlers will find themselves having to explain everywhere that they go that their dog is a service dog.

Most Common Reasons Listed For Service Dog Needs.
Asthma (or other breathing problems) Allergy Alert Blindness (& partial blindness)Cancer Deafness (& partial deafness) Cardio Vascular Stroke Diabetes Dizziness/Balance problems Epilepsy General Hearing Difficulty Mobility Problems Neurological Problems Paralysis Physical Weakness Speech Problems SeizuresGeneral Medical Alert

Service dogs can be trained by their owners or in any other manner the owner desires to assist them with their disability.

Emotional support dogs are dogs that provide comfort and support in forms of affection and companionship for an individual suffering from various mental and emotional conditions.

Most Common Reasons Listed For Emotional Support Dog Needs.

Anxiety Depression Bipolar disorder Mood disorder Fear/phobias Post-Traumatic Stress Disorder Suicidal Thoughts/Tendencies Adjustment Disorders Generalized anxiety disorder Social anxiety disorder Panic disorder Post-traumatic stress disorder Separation anxiety Dissociative Disorders Factitious Disorders Eating Disorders Impulse-Control Disorders Mental Disorders Due to a General Medical Condition Neurocognitive Disorders Mood Disorders Neurodevelopmental Disorders Personality Disorders Psychotic Disorders Sexual and Gender Identity Disorders Sleep DisordersStress Somatoform Disorders Substance Related Disorders

Emotional support are not required to be trained or perform any specific task. 

Therapy dogs are dogs that are used to bring comfort and joy to those who are ill or under poor conditions, such as those who have been affected by a natural disaster. Many people are able to connect with dogs and feel the love that they provide, and this has a therapeutic effect on them. Therapy dogs are generally very calm and well-behaved, so that they do not upset or make uncomfortable those around them.

Therapy Dogs do not require any specific training.

A Companion dog usually describes a dog that does not work, providing only companionship as a pet, rather than usefulness by doing specific tasks. Many of the toy dog breeds are used only for the pleasure of their company, not as workers. Any dog can be a companion dog, and many working types such as retrievers are enjoyed primarily for their friendly nature as a family pet, as are mixed breed dogs. The American Kennel Club also offers a Companion dog title for judged dog obedience competitions.

Companion Dogs do not require any specific training.